1. Field of the Invention
The present invention relates to method and apparatus for determining fiber orientation, and more particularly to such a method and apparatus which is suitable for determining the fiber orientation characteristics of paper in a process of paper making.
2. Prior Art
To make paper of high quality, it is essential to determine paper quality as well as fiber orientation characteristics of the paper obtained as finished product. Devices for such determination are already well known from, for example Japanese patent application Disclosure Gazette No. Hei 4-57983 (1992-57983), disclosing a non-contact orientation meter, and Japanese patent application Disclosure Gazette No. Hei 4-113205 (1992-113205), disclosing a fiber orientation determining apparatus, both of which utilize incidence and reflection of a light beam on a surface of paper to be tested.
The apparatus disclosed in the above-mentioned Disclosure Gazette No. 1992-57983 generally comprises a projector. This apparatus also comprises a rotatable diaphragm mechanism having a slit through which the light beam projected from the projector is guided and thereby converted to a narrow linear light beam (i.e., band-like light beam) with a variable longitudinal direction. A single light receiver is adapted to catch the band-like light beam which has been incident upon the paper surface at a predetermined angle and then reflected by the paper surface. In view of the fact that the maximum reflection factor is reached when the longitudinal direction of the bandlike light beam comes in coincidence with the fiber orientation (i.e., fiber orientation angle), the differential reflection factor with respect to the band-like light beam having the variable longitudinal direction is determined to calculate the fiber orientation index value characterizing the measure of the fiber orientation.
The apparatus disclosed in the above-mentioned Disclosure Gazette No. 1992-113205 generally comprises a projector and a rotatable sample carriage on which the paper to be tested is set and illuminated with the light beam projected from the projector. A single light receiving means is adapted to catch the light beam reflected by the paper surface. The fiber orientation index value and the fiber orientation angle are calculated from the intensity of the reflected light beam and a rotating angle of the sample carriage.
The primary purpose of paper fiber orientation characteristics is to determine the quality of the paper, which information is used to control the quality of the paper. It is therefore desired that such determination can be carried out in an online mode during the process of paper making. For example, in a paper machine comprising a wire part, a press part and a dryer part, it is important that the result of such determination should be effectively reflected in a material supply to the wire part, as well as a change in the operation of the wire part. This is important because the definite orientation characteristics of the paper are substantially given when the material dispersed in water is supplied to the wire part and during conveyance of the material along the wire part.
However, none of the above-mentioned fiber orientation determining apparatuses of prior art is suitable for such on-line determination since they include the rotatable members which employ time consuming processing. Additionally, with the apparatus disclosed in the above-mentioned Disclosure Gazette No. 1992-1113205, involving rotation of the sample carriage, it is impossible to rotate the paper web in a process of paper making. In this apparatus, the optical system comprising the projector means and the light receiving means might be rotated instead of the sample carriage to obtain an equivalent optical effect. However, the paper web will continue to move during rotation of the optical system and consequently the point to be measured also moves, so it is difficult to measure the same point, and thereby to accurately determine the fiber orientation of the paper web moving in the paper machine. Also, with the apparatus disclosed in the above-mentioned Disclosure Gazette No. 1992-57983, the band-like light beam is rotated, making it difficult to accurately determine the fiber orientation of the paper web moving in the paper machine.